This application is based upon and claims priority from prior French Patent Application No. 98-16367, filed Dec. 23, 1998, the entire disclosure of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to electronic circuits, and more specifically to a configurable electronic circuit whose function can be customized for a specific application.
2. Description of Related Art
While a standard circuit has a function that is defined and completely described in a data book published by the semiconductor manufacturer (i.e., founder), a configurable (or semi-specific) circuit is a circuit whose function can be customized for a specific application. Semi-specific circuits are also distinguishable from specific circuits because specific circuits are obtained by assembling cells that are designed and tested beforehand and use libraries of cells and hardware and software that enable their customization (these are known as pre-characterized circuits). Unlike such pre-characterized circuits, semi-specific circuits are prefabricated and require no additional technological step for customization. This customization may be done by the founder himself or by the final user using simple and low-cost methods.
Thus, for the manufacture of a semi-specific circuit, a distinction must be made between the prefabrication, which alone requires technological steps using appropriate masks, and the customization. The customization of a semi-specific circuit consists of setting up connections so as to impose certain potentials on particular nodes of the circuit (a node being the intersection between two meshes as defined under Kirchoff""s laws), especially a ground potential or a supply potential. The value of the supply potential corresponds to the value of a supply voltage that is referenced with respect to the ground. In the following description, the term xe2x80x9cconfigurationxe2x80x9d designates the customizing of the circuit and the term xe2x80x9cconfiguration nodexe2x80x9d designates a node of the circuit on which a specified potential may be imposed through the configuration.
Typically, the configuration is accomplished by the destruction of fuses. A fuse is an essentially capacitive bipolar component having a dielectric that is irretrievably destroyed when a sufficiently high voltage is applied to the terminals of the component. Through this destruction, the component becomes essentially resistive. The voltage required for this destruction is called a disruption or breakdown voltage, and thus the term xe2x80x9cbreakdownxe2x80x9d is also used to designate the destruction of the fuse. However, in the following description and in accordance with the present invention, the term xe2x80x9cfusexe2x80x9d is meant to cover all technical equivalents of such a component that can be envisaged by one of ordinary skill in the art. For example, the term xe2x80x9cfuse xe2x80x9d covers a junction.
The destruction of a fuse requires the generation of a breakdown voltage that is obtained by raising the supply voltage of the circuit, which is generally 3 or 5 volts. The breakdown voltage applied to the terminals of the fuse gives rise to the circulation of a high current between the terminals, and this destroys the fuse at a rate that may be relatively fast or slow. The configuration of an electronic circuit by the disruption or breakdown of the fuse is therefore an operation that entails current consumption and a certain duration. It is advantageous to reduce these two parameters.
It is an object of the present invention to reduce the time and/or current that is required for destructing fuses during the configuration of a configurable electronic circuit.
Another object of the present invention is to provide a configurable circuit in which a reduced number of fuses have to be destroyed during configuration.
One embodiment of the present invention provides a configurable electronic circuit having configuration nodes. Each of the configuration nodes is coupled to corresponding first means that is non-modifiable during configuration and second means that is modifiable during the configuration. The non-modifiable first means selectively imposes one of at least a first potential and a second potential on the configuration node prior to configuration, and the modifiable second means allows modification of the potential imposed on the configuration node by the non-modifiable first means. In a preferred embodiment, the modifiable second means includes at least one fuse that is in an intact state before configuration and that can be changed to a destroyed state after configuration.
Another embodiment of the present invention provides an information processing system that includes at least one configurable electronic circuit having configuration nodes. Each of the configuration nodes is coupled to corresponding first means that is non-modifiable during configuration and second means that is modifiable during the configuration. The non-modifiable first means selectively imposes one of at least a first potential and a second potential on the configuration node prior to configuration, and the modifiable second means allows modification of the potential imposed on the configuration node by the non-modifiable first means. In one preferred embodiment, the non-modifiable first means includes a sequence of p series-connected inverters, and a connection connecting the configuration node to either the output of the pth inverter or the qth inverter of the sequence, where q is an odd number that is less than p.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention.